Allergic Conjunctivitis: This is the most common cause of eye redness and itching, often associated with other allergic symptoms such as sneezing, runny nose, and itching of the ears or throat. It is usually bilateral and can be triggered by allergens like pollen, dust mites, or pet dander.

Dry Eye Syndrome: This condition can cause eye redness, itching, and a sensation of grittiness in the eyes, often due to inadequate tear production or poor tear quality.
Blepharitis: Inflammation of the eyelids can lead to redness, itching, and swelling, often associated with crusting around the eyelashes.
Conjunctivitis (Viral or Bacterial): While less likely to cause itching, viral or bacterial conjunctivitis can cause significant eye redness, discharge, and sometimes itching, especially in the case of viral conjunctivitis.

Acute Angle-Closure Glaucoma: Although rare, this condition is an emergency and can present with severe eye pain, redness, blurred vision, and sometimes itching due to the acute increase in intraocular pressure.
Keratitis (Corneal Ulcer): An infection or inflammation of the cornea can cause severe eye pain, redness, and vision loss, with itching being a less common symptom.
Uveitis: Inflammation of the uvea can cause eye pain, redness, sensitivity to light, and vision problems, with itching being an occasional symptom.

Ocular Rosacea: A condition characterized by inflammation of the eyes and eyelids, often associated with skin rosacea, causing redness, itching, and burning sensations.
Sjögren's Syndrome: An autoimmune disorder that can cause dry eyes and mouth, sometimes presenting with eye redness and itching due to decreased tear production.
Trachoma: A rare infectious disease caused by Chlamydia trachomatis, leading to chronic keratoconjunctivitis, which can cause eye redness, itching, and potentially lead to blindness if left untreated.